1. Field of the Invention
The invention relates to a light source for a rotating indicator device, that is a means for all-around display of a picture. Such a means for all-around display is disclosed in EP-A-208283. This European Patent Application as well as PCT/CH88/00098 and the Patent Application "Rotatable means for the visualisation of an image over an angle of 360.degree. " filed on the same day as the present Patent Application are considered to be disclosed for the purposes of this description.
2. Description of the Related Art
EP-A-208283 describes the principle of the means, while PCT/CH88/00098 indicates improvements and specifications of the grid. The Patent Application "Rotatable means for the visualisation of an image over an angle of 360.degree." is concerned with a specific embodiment of the drive system.
The few previously known means corresponding to the above mentioned publications function well, in view of the technical improvements already carried out and corresponding to the Patent Applications mentioned at the outset.
However, in realising the means according to the Patent Applications mentioned at the outset, a long-unexplained phenomenon was observed, this phenomenon being found troublesome by many users: the image visible all around exhibited wave-like fluctuations in its brightness and luminous intensity. Instability of the motor speed was thought to be a cause of this fluctuation. The Applicant then carried out various tests on the speed stability and found for the first time that the light fluctuations observed were due not--as assumed for a long time by the specialists--to instability of the motor speed but rather to interference phenomena of the previously used light sources or their light output fluctuating at the frequency of the mains alternating current, which light output having no recognisable importance in normal operation of such a light source outside the means according to the invention.